There are widespread concerns that current trends in resource-use are unsustainable, but the possibilities of overshoot/collapse vs. long-term sustainability remain under-theorized and controversial. It is common to portray human history as a relentless and inevitable trend toward greater levels of population and socioeconomic complexity. However, cycles of rise and collapse have occurred frequently in history, often followed by centuries of economic, intellectual, and population decline. A brief historical review of collapses suggests that the process of rise-and-collapse is actually a recurrent cycle found throughout history and in every region of the world. While many different natural and social phenomena have been invoked to explain specific collapses, a general explanation remains elusive.

In this project, we built a human population dynamics model by adding Accumulated Surplus and Economic Inequality to a predator–prey model of humans and nature, and used this model to investigate the potential mechanisms that can explain these cycles found in the historical record. We explain the model structure and simulated scenarios that offer significant implications. Four equations describe the evolution of Elites, Commoners, Nature, and Wealth. The model shows Economic Stratification or Ecological Strain can independently lead to collapse, in agreement with patterns in the historical record.

Mechanisms leading to two distinct types of collapses are discussed, one driven by the disappearance of labor, and the second by the exhaustion of nature. The measure “Carrying Capacity” is developed and its estimation is shown to be a practical means for early detection of a collapse. The model is not intended to describe actual individual cases, but rather to provide a general framework that enables carrying out "thought experiments" for the phenomenon of collapse and, importantly, to test changes that could avoid it. Comparisons are made with historical cases. Results show that collapses can be avoided, and population can reach a steady state at maximum carrying capacity if the rate of depletion of nature is reduced to a sustainable level and if resources are distributed equitably.